The mesmerizing wart: the pollination strategy of epiphytic lady slipper orchid Paphiopedilum villosum (Lindl.) Stein (Orchidaceae)

Paphiopedilum uillosum was studied in hill evergreen forests (at up to 35 m above ground level) in North Thailand between 1990 and 1994. Flowering lasted 4.5 months: flower longevity 2–3 months. During 224 hours of flower-watching, less than 100 specimens of Syrphidae (Diptera) were seen in the vicinity of the flowers; 15 cases of pollen acquisition were mainly by female Eplsyrphus alternans, Syrphus fulvifacies, Betasyrphus serarius among 6 spp. of pollinators. Populations peaked during the main flower opening period, one month before the maximum number of open flowers was reached in early February. The flowers are 'kettle-traps' without known reward, luring mainly by food deception. Long distance attraction is probably by a urine-like odour (attraction to mammalian excretions had hitherto been little reported) and colour contrast. Close range lure is by the glittering staminode (probably mimicking droplets of honeydew/moisture) centred by a slippery wart (faking a perch) at which pollinators fly, immediately losing their grip and tumbling into the pouch, preventing wing action and falling being disrupted by a trough-shaped frame. Escape is up the tunnel, past the stigma, to the exit where, pressed by several mechanisms against the anther, the hoverfly scoops off very sticky pollen which has a viability of at least 8 weeks. Capsule formation averaged 8%.